Field
The present application relates to spinal fixation devices. More specifically, the present application is directed to a polyaxial vertebral anchor assembly with vertical adjustment and split lock.
Brief Discussion of Related Art
Spinal fusion and/or deformity corrective surgery often requires securing various implants to the vertebrae. One of such implants is a pedicle screw and its related components. Pedicle screws are secured to the vertebrae involved in the surgery. The components, such as one or more stabilizing rods, are then secured to the pedicle screws via respective rod-holder assemblies in order to reduce or eliminate movement between and among neighboring vertebrae necessary for spinal fusion and/or deformity correction.
Because of the complex curvature and anatomy of the spine (e.g., lordosis), it is difficult to align certain pedicle screws and their associated rod-holder assemblies with the stabilizing rod, particularly when spanning multiple vertebrae. More specifically, the anatomy of the spine in individual patients makes it difficult and often impossible to align the pedicle screws in a single plane. The pedicle screws generally project with variable medial-lateral displacements and different angulations.
Traditionally, this type of alignment required extensive bending and test fitting (e.g., contouring) of the stabilizing rods to correctly approximate and connect to the rod-holder assemblies of the respective monoaxial pedicle screws.
More recently, polyaxial pedicle screws have enabled the rod-holder assembly to pivot about the pedicle screw's head. Such pivoting allows the rod-holder assembly to interface the stabilizing rod with minimal contouring of the stabilizing rod. Polyaxial pedicle screws have become widely available and are now the most common type of pedicle screws used in spinal fusion and/or deformity corrective surgeries.
While a polyaxial pedicle screw enables its associated rod-holder assembly to pivot about the pedicle screw's head, the rod-holder assembly engages the stabilizing rod in a fixed vertical relation to the pedicle screw's head. Accordingly, when multiple polyaxial pedicle screws are situated at substantially different heights along the vertebrae of the spine, certain pedicle screws that are lower than the other pedicle screws are unnecessarily stressed in order to bring their associated rod-holder assemblies toward the stabilizing rod.
In deformity corrective surgeries, pedicle screws are often used to straighten out the spine. More specifically, pedicle screws are used to manipulate the spine, which can involve rotating and translating the vertebrae of the spine in relation to the stabilizing rod. However, a polyaxial screw does not allow de-rotation of a vertebra because the head of the polyaxial pedicle screw is mobile in relation to the attachment of the pedicle screw to the vertebra. More specifically, the polyaxial pedicle screw provides no mechanism to engage the head of the polyaxial pedicle screw in order to rotate or translate the vertebra in relation to the articulating rod.
Moreover, the polyaxial pedicle screw does not provide vertical travel of the rod-holder assembly between the pedicle screw's head and the stabilizing rod for incremental connection to the stabilizing rod at multiple vertical locking positions. Although the polyaxial pedicle screws can be translated along the stabilizing rod (e.g., compression or distraction) to engage or connect to the stabilizing rod, they become much less flexible or useful in pulling or pushing the spine toward the stabilizing rod (e.g., reduction) when translated along the stabilizing rod.
More specifically, a surgeon can place one or more selected polyaxial screws strategically deeper or more superficially into the vertebrae of spine with respect to the stabilizing rod, as may be required for a certain deformity correction. As the stabilizing rod is delivered and tightened to the pedicle screw's associated rod-holder assembly, the pedicle screw will be pushed or more commonly pulled toward the stabilizing rod. However, because the polyaxial pedicle screw provides only one vertical locking position, the deficiencies in the manipulation of the vertebrae in the spine and associated connection to the stabilizing rod are more pronounced, requiring greater surgeon skill and surgical time for the spinal fusion and/or deformity corrective surgery.